Froth flotation method

ABSTRACT

A novel reagent, useful for depressing minerals during froth flotation, is obtained by mixing a solution containing complexed polyvalent metal cations, e.g., a solution containing Cu (NH3)4 2, with a solution of sodium or other alkali metal silicate to form a hydrosol.

United States Patent [191 Marsh Dec. 23, 1975 FROTH FLOTATION METHOD [75] Inventor: Gary B. Marsh, Woodbridge, NJ.

[73] Assignee: Engelhard Minerals & Chemicals Corporation, Edison, NJ

[22] Filed: Nov. 27, 1974 [21] Appl. No.: 527,684

[52] U.S. Cl. 75/2 [51] Int. Cl. C22B 1/00 [58] Field of Search 75/2, 67; 209/166, 167

[56] References Cited OTHER PUBLICATIONS Newton, Extractive Metallurgy, pp. 96-104 (John Wiley & Sons, 1967).

Primary Examiner-Peter D. Rosenberg Attorney, Agent, or FirmMelvin C. Flint; lnez L. Moselle [57] ABSTRACT 5 Claims, No Drawings FROTH FLOTATION METHOD BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the froth flotation of ores in which undesired minerals tend to float along with desired minerals because of close similarities in flotation characteristics. In particular, the invention relates to a novel depressing reagent composition and its use in froth flotation employing a fatty acid collector reagent.

It is well known that fatty acids such as oleic acid are effective as collectors in the froth flotation of a wide variety of nonsulfide minerals. To obtain adequate selectivity it is frequently necessary to include a depressant in the flotation circuit. The depressant prevents flotation of minerals other than those to be floated. Common depressants are sodium silicate and quebracho. In some cases common depressants are not sufficiently effective. This may occur when flotation is used to separate a mineral from one or more minerals having very similar flotation properties. A prime example of the ineffectiveness of common depressant may be encountered in attempts to separate fluorite (CaF from calcite (CaCO with an oleic acid collector. Another example is the flotation separation of scheelite (calcium tungstate) from calcite. An extremeexample is the flotation of fluorite from fluorapatite, both of which contain calcium and fluorine.

2. Prior Art It has been suggested to use various polyvalent metal salts along with sodium silicate to depress selectively minerals such as calcite which tend to be co-floaters with chemically similar minerals such as scheelite and fluorite. Ferrous sulfate, aluminum sulfate and copper sulfate are exemplary of metallic salts that have been proposed. In some cases, the salts are added to the pulp separately from the silicate. Others have proposed to mix the salt solution and the silicate solution before adding them to the flotation pulp. It has also been proposed to effectuate the depressing action of the metal salt by incorporating salts of molecularly dehydrated phosphates (polyphosphates) in the flotation pulp.

THE INVENTION An object of the invention is to provide a novel depressant reagent composition for use in fatty acid flotation.

Another object is to provide a depressant reagent composition which is more effective than known reagents in difficult selective flotation separations, exemplified by the flotation of fluorite from fluorapatite.

Stated briefly, the essence of my invention resides in a novel dilute stable alkaline hydrosol, useful as a flotation depressant, which is obtained by mixing an aqueous solution of complexed polyvalent metal cations and an aqueous solution of alkali metal silicate. A preferred reagent mixture, in accordance with this invention, is obtained by mixing a dilute solution containing complexed copper cations in the form of Cu(Nl-I (tetrammine copper (ll) cations) with a dilute solution of sodium silicate.

The hydrosols of the invention are generally useful in soap flotation of ores in which itis difficult to obtain desired selectivity with conventional depressants. Thus, the hydrosols are useful in the selective flotation of a calcium-bearing mineral such as fluorite from one or more calcium-bearing gangue minerals and/or calcium- DETAILED DESCRIPTION One class of complexed polyvalent metal cations useful in producing the novel hydrosols are obtained by reacting a source of polyvalent metal cations with ammonia in aqueous media to form positively charged amine complex ions by attachment of non-ionic ammonia to the metal cations. An example of cations which form stable (feebly dissociated) amine complexes is cupric ions. In forming the tetrammine copper (ll) complex ion, the source of copper ions may be a soluble salt such as the sulfate, nitrate or chloride. Alternatively a poorly soluble copper compound (such as cupric hydroxide or carbonate) which is solubilized by ammonia complexation may be used. Other complexed polyvalent metal cations are obtained by reacting sources of polyvalent metal cations such as, for example, nickel, copper, iron, aluminum, cadmium and cobalt with alkali metal salts of polyphosphoric acids, alkali metal salts of polycarboxylic acids such as gluconic, tartaric, oxalic and citric, or alkali metal salts of lower alkyl-substituted amino acetic acids and alkali metal salts of hydroxy amino acids and mixtures thereof. An example is the complex formed by reacting a solution of a nickel salt with sodium dihydrogen phosphate. Recommended is the use of dilute solutions of complexed metal cations, e.g., solutions having a concentration of complexed metal salt of 1% by weight or less.

Various alkali metal solutions may be used to form the hydrosol. For reasons of economy, sodium silicate is usually employed as the alkaline silicate. However, soluble silicates of potassium, lithium or ammonium may also be employed. Commercial sodium silicate solutions having a SiO /Na O molar ratio of about 3.22, such as 0, have produced excellent results. Preferably the sodium silicate is diluted to a SiO concentration of 5% by weight or less before it is mixed with a solution of complexed metal salt. The hydrosols have a pH in the range of 9 to II, most usually about 10.

The hydrosols of the invention are highly sensitive depressants. Consequently simple routine experimentation will usually be required to determine the optimum proportions of metal salt, complexing agent and sodium silicate used to form the stable hydrosol. When the ratio of complexed metal salt to sodium silicate is too low, the effectiveness of the hydrosol as a depressant is minimized. When the ratio of complexing agent to metal to be complexed is to high, the ore pulp may be overdispersed when the hydrosol is incorporated. Suitable proportions of hydrosol to feed vary from ore to ore and can be determined by routine testing.

The invention is especially useful in separating fluoritc from apatite to produce, for example, an acidgrade fluorite concentrate from fluorspar ore. Consequently, the invention will be described with especial reference to its utility in this application. It will be 3 understood, however, that my invention is considered to have other utility and is not to be considered as being limited to separating fluorite from gangue including fluorapatite.

Acid-grade fluorite concentrates contain at least 97% CaF less than 0.5% P and less than 1.5% SiO Fluorite (CaF is readily floatedfrom ore pulps by using an oleic acid collector. However, ores which are sources of fluorite usually contain other calcium minerals such as calcite (CaCO which have flotation characteristics similar to that of fluorite. In order to obtain economical recoveries of fluorite concentrates of acceptable grade it is frequently necessary to depress co-floating min erals such as calcite and calcium-activated silica or silicates.

Some fluorspar ores contain apatite, a complex calcium fluorophosphate mineral of the approximate formula Ca F(PO Fluorite and apatite are both calcium fluorite minerals and have virtually the same flotation characteristics. When a fluorspar ore contains a significant amount of apatite, it presents a separation problem of unique difficulty because flotation conditions which favor the flotation of fluorite favor also the flotation of apatite. Reagents capable of depressing calcite are of limited utility in depressing apatite. Thus, the prior art reagent mixture of sodium silicate and aluminum sulfate which is eminently effective in depressing calcite may be unsatisfactory when the ore body also contains apatite. v

I have found, however, that even the combination of a phosphate salt and a reagent mixture of aluminum sulfate and sodium silicate with a fluorspar ore containing both'apatite and calcite in the gangue did not effect sufficient depression of apatite to result in a fluorite flotation concentration meeting the phosphorous speciflcation for an acid-grade product.

Applying the principles of my invention to a fluorspar ore containing 37.9% CaF 1.11% P, 27.3% SiO and 10.7% CaCO products meeting acid-grade specifications have been obtained at CaF recoveries above 85%. This entailed removal of more than half of the P values contained in the apatite impurity and more than 80% of the calcite. When a hydrosol obtained by mixing a dilute aluminum sulfate solution with sodium sodium silicate was substituted for the reagent mixture of tetrammine copper (ll) complex ion and sodium silicate, depression of apatite was inadequate. The phosphorous level of the product exceeded the maximum tolerable level of 0.5% and CaF grade of the fluorite concentrate was lower when the prior art reagent mixture was employed.

ln applying the principles of my invention to the flotation beneficiation of fluorspar ore, the ore is ground sufficiently fine to liberate the fluorite. The ground ore is pulped at a suitable concentration level, e.g., to 40% solids. The ground ore is then usually alkalized by additng soda ash, typically using from 1 to 10 lbs. soda ash per ton of ore, to increase pH to a value in the range of about 8.5 to 10. The pulp is then dispersed by adding a hydrosol of the invention, exemplified by copper-ammonia-alkali silicate hydrosol. Generally the hydrosol is used in an amount to provide the equivalent of 4 to lbs. alkali metal silicate per ton of ore and from v. to 2 lbs. per ton of metal complex salt. A source of phosphate ion may be used in amount in the range of about 0.2 to 2 lbs/ton. Oleic acid or other fatty acid collector is employed in amount within the range of about 0.1 to 3 lbs/ton, usually in the range of 4 0.5 to 1.5 lbs/ton. Flotation is carried out at a pH in the range of about 9.0 to 10.5. When necessary a frother is added.

The following examples are given to illustrate further the invention.

EXAMPLE I A hydrosol of the invention is prepared as follows from a solution containing tetrammine copper (11) ions and a solution of sodium silicate. To a 1% solution of CuSO .5l-l 12.5 cc. of concentrated Nl-l OH is added to a total value of 262.5 cc. Dark blue coloration indicates the presence of the complex. A 20 cc. portion of the copperamine complex solution is mixed with 25 cc. of 0 sodium silicate solution previously diluted with water to 5% 0 concentration. A stable dark blue hydrosol, free from a perceptible precipitate, is obtained.

EXAMPLE II This example illustrates the use of the hydrosol of Example I to depress fluorapatite and calcite in the flotation of fluorite from a spar ore. Chemical analysis of the ore was as follows (wt. basis): CaF 37.91%; P 1.1 1%; Total SiO 32.80%; Free SiO 27.2%; CO 4.71%; S 0.10%. Mineralogical investigation revealed that quartz and calcite were the most abundant diluents in the fluorite. Apatite, present as fluorapatite, was the third most abundant. Mineralogical testing revealed that fluorite was substantially liberated from fluorapatite at 200 mesh (Tyler) and essentially complete liberation of fluorite from calcite and quartz occurred at 325 mesh.

The feed for flotation was a minus 325 mesh product prepared by wet grinding at 50% solids in a rod mill. The ground ore (250 g. charge) was diluted to 25 to 30% solids and dispersed by adding a 5% solution of soda ash in amount corresponding to 6 lbs. Na CO per ton ore. The pH of the pulp was 10.3. In accordance with the invention the hydrosol of Example 1 was added to the pulp in amount corresponding to 4.64 lbs/ton Cu(N1-l .,),,SO and 5.32 lbs/ton sodium silicate (dry weight basis).

Potassium dihydrogen phosphate was added as a 1% solution in amount corresponding to 1.68 lbs./ton. Dilute sulfuric acid was added to reduce pH to 9.5.

Sulfides were first floated in a Denver cell using 0.25 lbs/ton potassium xanthate amyl collector (Z-6") and Dowfroth 250. The tailings from the sulfide flotation were then conditioned in a Fagergren cell for flotation of fluorite by adding oleic acid in amount of 1.2 lbs/ton of the original minus 325 mesh feed and agitating the pulp intensively for 12 minutes. A fluorite rougher flotation was carried out in a Denver cell using pine oil frother. The rougher concentrate was cleaned three times by flotation without adding more collector. The products from the flotation tests were filtered, dried and weighed. Chemical tests were performed on the fluorite concentrate. The flotation concentrate, representing 34.6% by weight of the feed, assayed 96.1% by weight CaF (fluorite); 2.35% by weight Ca F(PO (fluorapatite); 0.46% FeCO 1.18% CaCO and 0.33% SiO The concentrate analyzed 0.48% P; 0.33% SiO and 1.57% CaCO ..Recovery of CaF was 87.7% by weight.

EXAMPLE lll A complexed nickel-silicate hydrosol of the invention is prepared by mixing 2.5 liters of a 1% aqueous solution of NiCl .6H O with 0.3 liter of a 5% aqueous solution of potassium dihydrogen phosphate. sodium silicate solution (9.l6% wt. Na O, 29.5 wt. SiO is diluted to 0" concentration with water. The solution containing complexed nickel ion is added with mixing to 2.5 liters of the diluted silicate solution. This forms a stable hydrosol.

I claim:

1. In the flotation separation of a calcium-bearing mineral from an ore wherein an ore pulp is dispersed with a soluble alkali silicate, a polyvalent metal salt is used as a depressant for one or more gangue minerals, and a calcium-bearing mineral is floated with a fatty acid collector, the improvement which comprises adding the polyvalent metal salt and the alkali silicate to the pulp in the form of a dilute stable hydrosol obtained by adding to a solution of polyvalent metal salt an agent capable of complexing metallic cations in the salt to form stable complex cations and mixing the resulting solution with a solution of alkali metal silicate.

2. The method of claim 1 wherein the hydrosol is formed by mixing an aqueous solution containing polyvalent cations with an aqueous solution of a material selected from the group consisting of ammonia, alkali metal salt of polyphosphoric acid, alkali metal salt of polycarboxylic acid, alkali metal salt of lower alkylsubstituted amino acetic acid and alkali metal salt of hydroxy amino acid.

3. The method of claim 2 wherein the hydrosol is formed by mixing a solution containing Cu(N]-l cations with a solution of sodium silicate.

4. The method of claim 1 wherein the ore is a fluorspar ore containing calcite and apatite in the gangue and fluorite is floated while calcite and apatite are depressed by said hydrosol.

5. The method of claim 3 wherein the ore is a fluorspar ore containing calcite and apatite in the gangue and fluorite is floated while calcite and apatite are depressed by said hydrosol. 

1. IN THE FLOTATION SEPARATION OF A CALCIUM-BEARING MINERAL FROM AN ORE WHEREIN AN ORE PULP IS DISPERSED WITH A SOLUBLE ALKALI SILICATE, A POLYVALENT METAL SALT IS USED AS A DEPRESSANT FOR ONE OR MORE GANGE MINERALS, AND A CALCIUM-BEARING MINERAL IS FLOATED WITH A FATTY ACID COLLECTOR, THE IMPROVEMENT WHICH COMPRISES ADDING THE POLYVALENT METAL SALT AND THE ALKALI SILICATE TO THE PULP IN THE FORM OF A DILUTE STABLE HYDROSOL OBTAINED BY ADDING TO A SOLUTION OF POLYVALENT METAL SALT AN AGENT CAPABLE OF COMPLEXING METALLIC CATIONS IN THE SALT TO FORM STABLE COMPLEX CATIONS AND MIXING THE RESULTING SOLUTION WITH A SOLUTION OF ALKALI METAL SILICATE.
 2. The method of claim 1 wherein the hydrosol is formed by mixing an aqueous solution containing polyvalent cations with an aqueous solution of a material selected from the group consisting of ammonia, alkali metal salt of polyphosphoric acid, alkali metal salt of polycarboxylic acid, alkali metal salt of lower alkyl-substituted amino acetic acid and alkali metal salt of hydroxy amino acid.
 3. The method of claim 2 wherein the hydrosol is formed by mixing a solution containing Cu(NH3)4 2 cations with a solution of sodium silicate.
 4. The method of claim 1 wherein the ore is a fluorspar ore containing calcite and apatite in the gangue and fluorite is floated while calcite and apatite are depressed by said hydrosol.
 5. The method of claim 3 wherein the ore is a fluorspar ore containing calcite and apatite in the gangue and fluorite is floated while calcite and apatite are depressed by said hydrosol. 